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\begin{document}
\begin{equation*}
  \begin{bmatrix}
    (M+m) & - ml\cos\theta \\
    (J+ml^2) & - m l \cos\theta
  \end{bmatrix} \begin{bmatrix} \ddot p \\ \ddot\theta \end{bmatrix}
  + \begin{bmatrix} -b \dot p + ml \sin\theta\, \dot\theta^2 \\
    mgl\sin\theta
  \end{bmatrix} = \begin{bmatrix} F_b \\ 0 \end{bmatrix}
\end{equation*}
\end{document}